1. Field of the Invention
The present invention relates to a wireless selective call receiver with a speech notice function, and more particularly to a wireless selective call receiver with a speech notice function in which a power supply voltage is determined in a loading state.
2. Description of the Related Art
In recent years, there is widely used a wireless selective call receiver with a display function in which numeral information and message information are displayed at a liquid crystal display. In addition, a wireless selective call receiver with a speech notice function is also widely used in which a received information is noticed or outputted with speech. Further, as one of the functions of the wireless selective call receiver with a display function and a speech notice function, there is known a speech record function in which a received pattern of specific numerals and/or symbols is displayed as a message sentence and noticed with speech.
Such a wireless selective call receiver with the speech notice function needs a speech synthesis LSI for converting received message information into a speech signal, and an amplifier for amplifying the speech signal such that a speech message can be outputted from a speaker. Also, the wireless selective call receiver with the speech recorder function further needs a microphone, the above speech recording LSI and so on.
By the way, the conventional wireless selective call receiver uses a single dry battery cell as power supply. If the power supply voltage decreases, there is a case where system down occurs during the speech notice of a message. For this reason, the power supply voltage is checked. Such a first conventional wireless selective call receiver is disclosed in Japanese Laid Open Patent Disclosure (JP-A-Heisei 3-203419: the first reference).
FIG. 1 is a block diagram illustrating the structure of a second conventional wireless selective call receiver with a display function (the second reference). Referring to FIG. 1, the conventional wireless selective call receiver is composed of a reception antenna 1, a radio section 2, a decoder control unit 3, a message memory section 4, a display output control unit 5, a display driver 6, a display unit 7, a low voltage determining section 8, a timer 9, a DC/DC converter 10, a power supply section 11, and a reset switch (SW) 12.
The reception antenna 1 receives a radio signal which is transmitted from a base station. The radio section 2 demodulates the radio signal which is received by the reception antenna 1. The decoder control unit 3 compares the demodulated signal A and an own call number of the wireless selective call receiver. When the demodulated signal A is coincident with the own call number, the decoder control unit 3 stores a message signal B subsequent to the call number of the demodulated signal A in the message memory section 4. Also, the decoder control unit 3 outputs a coincidence signal E to the display output control unit 5. The reset switch 12 generates a trigger for starting or stopping the display. The display output control unit 5 issues a control signal F to the message memory section 4 in response to the trigger from the reset switch such that the stored message signal C is sent out to a display driver 6 and displayed on the display unit 7, when the coincidence signal E has been received from the decoder control unit 3. The power supply section 11 composed of a dry battery cell or a charged battery cell of 1.05 V to 1.5 V and the DC/DC converter 10 converts the output voltage of the power supply section 11 into a predetermined voltage. The output voltage of the DC/DC converter 10 is supplied to each of sections of the wireless selective call receiver. The low voltage determining section 8 performs a low voltage determination of the output voltage from the power supply section 11 for every predetermined time interval, using a timer 9. When the output voltage from the power supply section 11 decreases to a value lower than a predetermined level, a signal H indicative of the determining result of the low voltage is outputted from the low voltage determining section 8 to the display output control unit 5. In this case, a low voltage caution operation is started.
In the conventional wireless selective call receiver as described above, the low voltage determination of the battery cell of the power supply section 11 is performed in the state of almost no load. On the other hand, in the wireless selective call receiver with the speech notice function described in the first reference, a received message signal is processed by a speech synthesis LSI and an amplifier is driven such that a speech of message is outputted from a speaker. At this time, current of a few of hundreds milli-amperes flows. Therefore, if the message notice is performed as soon as the message signal is received, there is the possibility that any system down occurs before the low voltage determination is performed by the low voltage determining section. Especially, when a used battery cell of a high internal resistance is put into the wireless selective call receiver through cell exchange, the normal voltage is outputted for a moment and the receiver starts the operation. However, the battery cell voltage decreases abruptly to a value lower than the operation limit voltage of the DC/DC converter 10 when a speech notice is started. Therefore, it is expected that system down occurs.